The NIDCR K08 award will provide me with the opportunity to receive additional mentor supported training with the focus on establishing myself as an independent researcher in the future. Bone resorption is a central mechanism in skeletal development, remodeling and pathology. Resorption is mediated by osteoclasts, multinucleated giant cells that are derived from the monocyte/macrophage lineage. RANKL is a mandatory factor in inducing osteoclast differentiation, although the signaling pathways it activates are only partially understood. My previous work identified the Brn3 transcription factor family as downstream targets of RANKL. The activation of Brn3 factors reached a maximum concurrent with the first appearance of giant cells. Functional inhibition of Brn-3/POU-DNA binding activity using decoy oligonucleotides resulted in inhibition of osteoclast fusion and reduction in bone resorbing activity of mature osteoclasts. Mice with a targeted deletion of brnSb exhibited increased cortical as well as trabecular bone mass. These findings lead to the novel hypothesis that the function of Brn3 transcription factors is crucial for osteoclast differentiation and activity. Aim 1 of this grant application will determine the relative importance of each factor (BrnSa, b, c) in RANKL-induced osteoclast development and activity by using inhibition and overexpression studies. Aim 2A and 2B will identify specific Brn3-regulated genes and transcriptional mechanisms in osteoclasts through a systematic use of gene array techniques and 2-D protein separation combined with mass spectrometry. Aim 2C will further characterize these identified Brn3 target genes in their impact on osteoclastogenesis by silencing their expression. Aim 3 will determine the effects of Brn3 gene deletion in a model of pathologic periodontal bone resorption caused by bacterial infection. The overall goal is to characterize Bm3 transcription factors and their target genes that are present in osteoclasts, and determine their role in the regulation of bone under physiologic and pathologic conditions.